//给定两个整数数组 inorder 和 postorder ，其中 inorder 是二叉树的中序遍历， postorder 是同一棵树的后序遍历，请你构造并
//返回这颗 二叉树 。 
//
// 
//
// 示例 1: 
//
// 
//输入：inorder = [9,3,15,20,7], postorder = [9,15,7,20,3]
//输出：[3,9,20,null,null,15,7]
// 
//
// 示例 2: 
//
// 
//输入：inorder = [-1], postorder = [-1]
//输出：[-1]
// 
//
// 
//
// 提示: 
//
// 
// 1 <= inorder.length <= 3000 
// postorder.length == inorder.length 
// -3000 <= inorder[i], postorder[i] <= 3000 
// inorder 和 postorder 都由 不同 的值组成 
// postorder 中每一个值都在 inorder 中 
// inorder 保证是树的中序遍历 
// postorder 保证是树的后序遍历 
// 
// Related Topics 树 数组 哈希表 分治 二叉树 👍 736 👎 0

package leetcode.editor.cn;
//leetcode submit region begin(Prohibit modification and deletion)

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 * int val;
 * TreeNode left;
 * TreeNode right;
 * TreeNode() {}
 * TreeNode(int val) { this.val = val; }
 * TreeNode(int val, TreeNode left, TreeNode right) {
 * this.val = val;
 * this.left = left;
 * this.right = right;
 * }
 * }
 */
class Solution106 {
    //遵循原则：左闭右开
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        return buildTree1(inorder, 0, inorder.length, postorder, 0, postorder.length);
    }

    private TreeNode buildTree1(int[] inorder, int inLeft, int inRight,
                                int[] postorder, int postLeft, int postRight) {
        if (inRight - inLeft < 1) {
            return null;
        }
        if (inRight - inLeft == 1) {
            return new TreeNode(inorder[inLeft]);
        }
        //找根节点
        int rootVal = postorder[postRight- 1];
        TreeNode root = new TreeNode(rootVal);
        //找中序数组的切割点
        int rootIndex = 0;
        for (int i = inLeft; i < inRight; i++) {
            if (inorder[i] == rootVal) {
                rootIndex = i;
                break;
            }
        }
        root.left = buildTree1(inorder, inLeft, rootIndex,
                postorder, postLeft, postLeft + (rootIndex - inLeft));
        root.right = buildTree1(inorder, rootIndex + 1, inRight,
                postorder, postLeft + (rootIndex - inLeft), postRight - 1);
        return root;
    }
}
//leetcode submit region end(Prohibit modification and deletion)
